Kolarov was more like a left wing back. He never worked as well in a flat back 4 in my opinion - but, similar to Mendy, his crossing was brilliant and he couldn't half kick a ball.
Clichy was the most athletic and well rounded defender. Comfortable in possession too. Would be perfect in a Pep team.
Mendy just isn't good enough IMO. He's injury prone, he can't defend, he makes rash decisions. He's got a brilliant cross and can be useful when the other team parks the bus.
Zinchenko isn't even a left back. He's done really well covering that position, but he's clearly not a long term solution.